In order to perform observations with a higher resolution and a higher accuracy, telescope systems for performing astronomical observations by receiving observation light or radio waves from the space are getting larger and larger in recent years. In particular, the reflecting mirror unit in the telescope systems, whose aperture diameter is several meters to several tens of meters, has been considered, so that it has been necessary to more accurately support the reflecting mirror. For example, in Japanese Patent Application Laid-Open No. 118295/1994, a conventional reflecting-mirror supporting mechanism is described. In the reflecting-mirror supporting mechanism disclosed in Japanese Patent Laid-Open No. 118295/1994, a hole for fixing a supporting mechanism is provided in the reflecting mirror, and the point at which the reflecting mirror is supported by the supporting mechanism is located in the position of the center of gravity of the reflecting mirror. Thus, by supporting the reflecting mirror at the position of the center of gravity, moment load due to the displacement between the supporting point and the reflecting-mirror gravity center position is prevented from arising. Therefore, variations in the moment load, which arises from bearing change of the reflecting mirror such as change in the elevation angle, can be prevented, so that generation of stress in the reflecting mirror and change in shape of the reflecting mirror can be prevented.
In the conventional reflecting-mirror supporting mechanism, in order to support the position of the center of gravity of the reflecting mirror, the hole for fixing the supporting mechanism is formed in the reflecting mirror. However, there has been a problem in that milling for forming a hole in the base material of the reflecting mirror must be performed for each supporting point, so that machining man-hours increase, and the number of days required for the machining resultantly increases. In particular, the larger the aperture diameter of the reflecting mirror, the thicker the thickness of the base material of the reflecting mirror in order to ensure the rigidity. Therefore, it sometimes has taken about one year to perform machining of the supporting-mechanism fixing holes.    [Patent document 1] Japanese Patent Laid-Open No. 118295/1994